The Bosporus is gorgeous and stuffed with history - 5,000 years of history. I highly recommend this excursion not only for the history lesson but also for the excellent service and good food.
The day started a bit shakey when we met our guide at our hotel (Sura Hagia). We didn't climb into the van, instead he made us walk nearly a mile. From there we picked up one more guest than headed to the boat, however the van stopped half-way there to fill up on gas. Why would you stop to get gas when you have a van full of guests? Why not gas up before pickup?
That was the only negative, the rest of the day was wonderful. For clarity sake, you do not actually cruise into the Black Sea, the boat doesn't even pass the third bridge. Still, this was my highlight of Istanbul.